Hydraulic control for operating an automatic gearbox, especially a continuosly variable transmission

ABSTRACT

A hydraulic control for operating an automatic transmission, especially a continuously variable transmission, has at least one first and one second switching component (1, 2) for forward or reverse drive from a neutral position (N) to a drive (D) or reverse (R) position and vice versa. The switching components (1, 2) can be actuated by pressure via pressure lines (24, 25) by a selector slide (15) and by a switching device (26) between the selector slide (15) and the switching components (1, 2) which has a switching valve (27, 28) and a damper, switching and vent valve (29, 30) for a switching component (1, 2). The switching device (26) has a safety and vent device designed in a manner such that when one of the switching components (1, 2) is actuated, the other switching component(s) is/are automatically disengaged.

The invention relates to a hydraulic control for operating an automatictransmission including a CVT, having at least one first and one secondswitching component for forward or reverse drive from a neutral positionto a forward drive position or a reverse drive position and vice versa.

BACKGROUND OF THE INVENTION

As generally known from the practice, in automatic transmissions withhydraulically actuated switching components, which usually have aswitching piston installed in a piston space on a disc set to carry outa gearshift, the switching component is first filled with oil before theswitching piston is placed on the disc set. If the switching componentis disengaged, the pressurized medium is removed from the switchingcomponent and the disc set is again relaxed. The filling andinstallation of a switching component has a rapid filling phase in whichthe switching component that is almost full or running partly empty isfilled with oil, there follows a filling equalizing phase during which aswitching piston is placed on the disc set. At the end of the fillingequalizing phase follows a pressure increasing phase which can bereproduced as pressure ramp increasing in the course of time. Duringthis pressure increasing phase or pressure ramp the discs are adequatelypressed together and can transmit or receive a torque.

It also is generally known that in a first range up to the beginning ofthe pressure ramp a turbine belonging to a hydraulic start component ofthe transmission rotates at the idling speed of an engine connected withthe transmission. When the pressure ramp has been climbed, the speed ofthe turbine goes back to zero and a torque is passed, for example, tothe wheels of a motor vehicle wherein a jerky process generally occurswhich, as a rule, is felt as disturbing.

After the end of the pressure ramp, the pressure can be further raised,to increase torque transmission, by the switching components. The risein pressure is effected according to what is needed.

On the other hand, when the switching component is opened, for example,the turbine begins to rotate until it reaches the engine idle speed. Asa rule, the turbine can then take up in a manner such that this, inturn, is noticed by the driver as light jolt.

There have become known from testing that the gearshift operation can bemade more comfortable by using switching times which are as brief aspossible.

However, this raises questions, relative to safety, since in a changethat is too quick, under certain circumstances, two switching componentsare simultaneously loaded with pressure and work against each other,causing a lock up of the transmission. This can bring about a situationcritical to safety in addition to the operating comfort being greatlyreduced.

SUMMARY OF THE INVENTION

Therefore, the problem to be solved by the invention is to provide acontrol for operating an automatic transmission from a neutral positionto a forward drive position or a reverse drive position and vice versa,the same as reversal shifts forward drive position--reverse driveposition and vice versa with which a more comfortable, almost jolt-free,quicker and safer gearshift is obtained.

The control according to the invention makes it possible that the changebetween the neutral position and the forward drive position or reversedrive position and back, the reversal shifts to forward driveposition--reverse drive position and vice versa be so comfortable thatas a rule the occupants of a motor vehicle will not notice the gearshifteither by a switching jolt or by a noise.

In addition, it is possible with the control, according to theinvention, to keep the starting point of a pressure ramp constant duringpressure loading by the damper, switching and vent valve.

The control, according to the invention, offers the added advantage thatit is very quickly possible to make shifts between forward driveposition and reverse drive position wherein the switching components arereciprocally blocked in a manner such that, upon actuation of aswitching component, other switching components are automaticallydisengaged.

A quick vent of the unactuated switching components can advantageouslyprevent the occurrence of an operating state in which two switchingcomponents are simultaneously actuated, that is, there cannot occur anytransmission stress or head-on blockage of the switching componentswhich would cause a torque impact.

The control, according to the invention, contributes considerably to anincrease of the operating safety of a vehicle.

The quick vent of the switching components upon reversals is ensured bya very advantageous quick vent of the damper space of the switchingvalves, via the damper, switching and vent valve.

With the control, according to the invention, it is in addition possibleadvantageously to regulate, according to the torque to be transmitted,the pressure on a switching component even in operating state. Thecontrol, according to the invention, is further advantageous in thattolerances in the pressure loading of the switching components can becompensated.

Other advantages and advantageous developments of the invention resultfrom the sub-claims and the description that follows of an embodimentwith reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWING(S)

The drawing shows a basic representation of a hydraulic control,according to the invention, for an automatic transmission having twoswitching components for forward and reverse drive. A CVT transmission(continuously variable transmission) is also possible here.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawing, it shows a hydraulic control of an automatictransmission in a motor vehicle, the individual components of which are,to a great extent, of known design for which reason only the essentialfeatures will be discussed in detail.

To operate a switching component 1 and another switching component 2which are symbolically indicated in the drawing, system pressure is fedby a pump 3 to a hydraulic system. The system pressure is first set by afirst pressure-limiting valve 4 which is controlled by an electronicallycontrolled pressure regulator. The pressure-limiting valve 4 isconnected by a pressure line 5 with a hydraulically starting component6, only symbolically indicated, the oil supply of which is therebyensured. Together with the hydraulic starting component 6, consumers 7,indicated only symbolically, are supplied with system pressure, viapressure lines 8 and 9.

The system pressure to operate the switching components 1 and 2 of thehydraulic system is fed, via other pressure lines 10, 11, 12, therebeing situated in each line 10 and 11 a pressure-reducing valve 13, 14which reduces the system pressure to a constantly remaining output valuewhich is always lower than a minimum pressure adjustable by thepressure-limiting valve 4. In the instant embodiment, the outputpressures of the pressure-reducing valves 13 and 14 are equal but inanother embodiment they can also be different.

In the pressure line 12, which leads to a selector slide 15, is situateda clutch pressure valve 16 which regulates the pressure level on theswitching components 1 and 2. The clutch pressure valve 16 regulates thepressure loading of the switching components 1 and 2 in accordance withthe torque. Thus, it is possible to preset a torque-dependent pressure,via the clutch pressure valve 16, in the operation with a closedswitching component 1, 2. The clutch pressure valve 16 is controlled byan electromagnetically adjustable pressure regulator 17 with which theclutch pressure valve 16 is connected by a pressure line 18. Thepressure regulator 17 is a proportional valve which is actuated by acurrent supplement in a manner such that for each change of current, achange of the output pressure of the pressure regulator 17 also linearlyoccurs.

During a pressure buildup in one of the switching components 1, 2 whichis along an adjustable pressure ramp having a ramp gradient and a rampoperating time, the clutch pressure valve 16 remains unchanged. Thisapplies as long as no change of torque occurs on the engine during thegearshift operation.

During travel, the clutch pressure valve 16 takes over, in addition, thetask of a reverse drive lock, for which advantageously no othercomponents are needed. To this end, the clutch pressure is disengagedwhen changing the forward drive above a specific velocity of thevehicle.

To regulate a load valve 19 on which is applied, via the pressure line10, the output pressure of the pressure-reducing valve 13, the latter isconnected by a pressure line 20 with a pressure regulator 21 having aconstructional configuration identical to the pressure regulator 17which is coordinated with the clutch pressure valve 16.

From the pressure line 20, which connects the pressure regulator 21 withthe load valve 19, branches off another pressure line 22 for pressuresupply of other functions, not shown, such as for maintaining a certainpressure level in other hydraulic circuits of the transmission. Theconnecting pressure line 20 between the load valve 19 and the pressureregulator 21 and the connecting line 18 between the clutch pressurevalve 16 and the pressure regulator 17 are each connected, via apressure line 57, with the pressure-reducing valve 14, the constantoutput pressure of which is fed, via feed-in nozzles 55, 56, to thepressure lines 18, 20.

Depending on the position of the selector slide 15, five switchingpositions can be selected, namely, the switching positions D, L forforward drive, a switching position R for reverse drive, a switchingposition N for neutral position and a switching position P for parkingposition. The selector slide 15 is manually actuatable by a selectorlever 23. In the drawing the selector slide 15 is shown in neutralposition N which hydraulically considered is equivalent to the parkingposition P, since in both switching positions N and P the switchingcomponents 1 and 2 are vented.

From the selector slide 15, a pressure line 24 leads to the switchingcomponent 1 and a pressure line 25 leading to the switching component 2,there being situated between the switching components 1 and 2 and theselector slide 15 a switching device 26 which has, for each one of theswitching components 1 and 2, a respective switching valve 27 and 28 anda damper, switching and vent valve 29 and 30. The switching position ofthe switching components 1 and 2 is determined by the position of theselector slide 15, by the position of the switching valves 27, 28 and bythe position of the clutch pressure valve 16.

In addition, the selector slide 15 performs an emergency function incase of failure of the transmission control when the valves 17, 19 areno longer electrically controllable, since the switching components 1and 2 can be further actuated by the switching valves 27, 28, via apressure ramp. The reciprocal interlocking is maintained here. In anemergency the pressure loading of the switching components 1, 2 with amaximum clutch pressure is provided by the pressure regulator 17 and theclutch pressure valve 16 interacting therewith.

The switching valve 27 coordinated with the switching component 1 is inthe pressure line 24 and the switching valve 28 coordinated with theswitching component 2 is in the pressure line 25 intercalated betweenthe switching component 1 or 2 and the selector slide 15. The switchingvalves 27, 28 have in a respective valve housing 31, 31' a movable valvepiston 33, 33', a damper piston 40, 40' and a compression spring 38,38'. The damper pistons 40, 40' can be loaded here with a controlpressure which , via a pressure line 34 or 35, reaches from the damper,switching and vent valve 29 to the switching valve 27 or 28.

The valve housing 31, 31' of the switching valves 27 and 28 have each asupply of pressurized medium via the lines 24, 25 and a tank connection37, 37'.

In the valve housings 31, 31', between the valve pistons 33, 33' and thedamper piston 40, 40', in a working space 39, 39', is situated axiallymovably supported a prestressable spring 38, 38'.

A switching valve 27 or 28 is pressure loaded directly, via theappertaining damper, switching and vent valve 29 and 30 and at a momentwhen the appertaining switching component 1 or 2 is almost entirelyfilled with pressurized medium. The reversal point of the damper,switching and vent valve 29 and 30 is therefore slightly below a chargepressure of the appertaining switching component 1 or 2. A pressure rampon the switching component begins after reversal of the appertainingdamper, switching and vent valve 29, 30, for example, when the pressureof the switching component is substantially 0.2 to 0.3 bar below a finalfilling value. Thereby the pressure buildup is constant for all factorsaffecting an operating state such as temperature and oil viscosity. Whendisengaging the switching component 1 or 2 concerned, the oil volumecropping out behind the damper piston 40, 40' is directly removed, viathe appertaining damper, switching and vent valve 29 or 30 directly to atank 41, 41' whereby a quick vent is ensured.

The damper, switching and vent valves 29, 30 are designed in theembodiment, according to the drawing, as 3/2 slide valves and eachhaving a spring 42, 42' which determines the reversal value of therespective damper, switching and vent valve 29, 30 so as to counteract apressure on the switching component 1, 2 which has been fed, viapressure lines 43, 43' to the damper, switching and vent valve 29 or 30.The reversal value of the valve 29 or 30 is thereby function of thefilling pressure of the coordinated switching component. In theembodiment shown the springs 42, 42' have a different design and areadapted to the operating conditions. In another embodiment, similarsprings obviously can be used.

To prevent that two switching components from being simultaneouslyactuated, the switching device 26 has a safety and vent device whichensures that upon actuation of one of the switching components 1 or 2the other switching component is automatically disengaged. To this end,there branches off from the pressure line 24, between the selector slide15 and the switching valve 27 of the first switching component 1, acontrol pressure line 44 which introduces a control pressure on anactive surface of the valve piston 33' which is coordinated with the notselected switching component 2 whereby the valve piston 33' of theswitching valve 28 is moved to the left far enough so that the tankoutlet 37' of the switching valve 28 is opened. Thereby pressurizedmedium is directly removed to the tank 37' from the unactuated switchingcomponent 2. The pressure line 44, which branches off from the pressureline 24, is in addition connected with the damper, switching and ventvalve 29, of the selected switching component 1 and via the componentand the pressure line 34 feeds pressurized medium to the switching valve27 in a manner such that the damper piston 40 of the switching valve 27,within a time determined by the feed-in nozzle 46, moves to the rightand thereby continuously prestresses the compression spring 38. From thecontinuously increasing spring compression upon the left side of thevalve piston 33 there is produced in the interplay with the reducedpressure of the switching component 1, which engages an active surfaceon the right side of the valve piston 33, the pressure ramp needed tooperate the switching component. The switching component 2 is hereautomatically vented.

If the switching component 2 is selected and must be actuated, it issimilarly loaded with pressure and the switching component 1 is locked.

The safety and vent device thus ensures a reciprocal locking since whileloading with pressure one of the switching components 1 or 2, theswitching valve of the unactuated switching component is loaded withpressure in opposite direction so that in a reversal a quick vent of theother switching component by force takes place.

The supply of control pressure, via the control pressure lines 44 and 45to the respective damper, switching and vent valve 29 or 30 is throttledby a nozzle 46 and 47 which determines the definite operating time ofthe ramp.

In the working space 39, 39' of the spring 38, 38', the load pressure isfed, via a pressure line 48, by the load valve 19.

From a balance of the forces on the switching valves 27, 28 can bedetected, for example, that the pressure of the switching component 2 ismomentarily proportional to the load pressure of the loading valve 19during the damper operating period. The pressure on the switchingcomponent 2 is likewise proportional to the spring tension of the spring38' in the switching valve 28 belonging to the switching component 2.This means that in consequence of a change in the prestress of thespring 38' an increase of the pressure in the coordinated switchingcomponent 2 occurs, that is, a change of path on the spring constitutesa change of pressure or basic ramp. The spring prestress is increased,according to the volume flowing in, whereby the pressure increases onthe switching component concerned.

The pressure originating from the loading valve 19 depends on an engineload and is altered by the pressure regulator 21. The loading valve 19acts with its output pressure, via the pressure line 48, upon bothswitching valves 27, 28 or the valve piston 33, 33' thereof. Thereby thepressure ramps produced by said switching valves in the appertainingswitching component 1 or 2, for example, can be changed in a manner suchthat the pressure ramp extends with equal gradient to a higher pressurelevel. In this manner, the switching components 1, 2 are supplied withpressurized medium according to the load.

The vent of the switching components 1, 2 on the switching valves 27, 28takes place when reversing via the respective tank connection 37, 37'When switching back from forward position or reverse position afterneutral or parking position, the corresponding switching components arevented via the selector slide 15 and the draining nozzles 53, 54 in thetank 51, 52.

The beginning of the pressure ramp is determined by the pressure fed tothe switching valve 27 or 28 by the respective damper, switching andvent valve 29 or 30 via the pressure line 34 or 35. On the other hand,the load pressure of the loading valve 19 serves for a change of thepressure loading of the valve piston 33, 33' in the switching valves 27,28, for example, when the load change occurs by gas supply during thegearshift.

By the load pressure of the loading valve 19, a comfortable gearshiftcourse can be represented even when shifting from the neutral position Nto the forward drive position D or L or to the reverse drive position Runder an engine part load.

If the selector slide 15 is in neutral position N or parking position P,both switching components 1 and 2 are vented by removing the pressurizedmedium from the switching components via the selector slide 15 andpressure lines 49 and 50 to a pressurized-medium tank 51 or 52. Betweenthe selector slide 15 and the pressurized-medium tank 51 or 52 is placeda draining nozzle 53 or 54 which adjusts the cross section of thethrough flow for the drain of the pressurized medium in accordance withthe temperature of the transmission. Corresponding to the higher oilviscosity at low temperatures or low oil viscosity at high temperatures,the draining nozzles 53, 54 change their cross section in such a mannerthat at low temperatures large drain cross sections and at hightemperatures small drain cross sections are adjusted. By thetemperature-dependent adjusting function, which is obtained by anytemperature-dependent setting or adjustment members (not shown), thedischarge time of the switching components 1, 2 can be maintainedconstant over the transmission temperature range.

On the other hand, when shifting directly from forward drive to reversedrive, no delay of the pressure breakdown occurs in the switchingcomponents 1, 2 by the draining nozzles 53, 54, since this would cause ajolt which impairs the gearshift quality. The switching components 1, 2are drained here via the tank connections 37, 37' on the switchingvalves 27 and 28.

We claim:
 1. A hydraulic control in an automatic transmission having atleast first and second switching components (1, 2) with which iseffected a gearshift from a neutral position (N) to a forward driveposition (D), reverse drive position (R), parking position (P) or otherswitching positions for forward and reverse drive and having a hydraulicsystem with pressure lines and with the following features:a) saidswitching components (1, 2) are actuatable with pressure which is fedvia pressure lines (24, 25) connected with a selector slide (15); b)said switching device (26) has a switching valves (27, 28) contained invalve housings (31, 31'), for each switching component (1, 2), saidvalve housings (31, 31') of said switching valves (27, 28) beingsupplied with pressurized medium via a respective pressure line (24, 25)and having a tank connection (37, 37') wherein: c) each of saidswitching valves (27, 28) is coordinated with a damper-switching andvent valve (29, 30); d) each of said switching valves (27, 28) has inthe respective valve housing (31, 31'), a movable valve piston (33, 33')and a damper piston (40, 40') and a spring (38, 38') wherein said damperpiston can be loaded with a control pressure which is supplied by therespective damper, switching and vent valve (29, 30) connectable withthe particular switching valve (27, 28); e) said switching device (26)has a safety and vent device designed so that upon actuation of one ofsaid switching components (1, 2) the other switching component isautomatically disengaged; andwherein a control pressure which engages anactive surface of said valve piston (33, 33') of the switching valve (28or 27) belonging to the switching component (2 or 1) not selected, issupplied, via a control pressure line (44 or 45) in a manner such thatrespective tank connection (37, 37') is opened, said control pressurealso discharges in the damper, switching and vent valve (29, 30)belonging to the selected switching component (1 or 2) in such a mannerthat said respective damper piston (40, 40') thereby loaded withpressure produces by continuous prestress of the respective spring (38,38'), a pressure ramp needed for switching the corresponding switchingcomponent.
 2. The device according to claim 1, wherein each of saidswitching valves (27, 28) has on one side of its valve piston (33, 33')the respective prestressable spring (38, 38') within a working space(39, 39') defined at one end of said spring (38, 38') by the valvepiston (33, 33') and at an opposing end of said spring by the damperpiston (40, 40'), the damper piston being axially moveable andsupporting said spring (38, 38') in the valve housing (31, 31').
 3. Thedevice according to claim 2, wherein the prestress of said spring (38,38') in each of said switching valves (27, 28) and the positioning ofsaid valve piston (33, 33') connectable with said spring are adjustablein a manner such that the pressurized medium fed to each of saidswitching components (1, 2) and the control pressure from the respectivecontrol line (44, 45) act on the other side of said valve piston, andsaid one side of said valve piston facing said spring (38, 38') isloaded with a pressure composed of a pressure passed into the workingspace (39, 39') of said spring (38, 38') via a pressure line (48) from aload pressure valve (19) and another pressure is passed to the side ofsaid damper piston remote from said spring via a pressure line from thedamper, switching and vent valve coordinated with the respectiveswitching valve.
 4. The device according to claim 1, wherein each ofsaid damper, switching and vent valves (29, 30) and coordinatedswitching valve (27, 28) can be loaded with pressurized medium directlyat a specific pressure of the respective switching component (1, 2). 5.The device according to claim 1, wherein the supply of pressurizedmedium from one of the control pressure lines (44, 45) to the respectivedamper, switching and vent valve (29, 30) is throttled by a nozzle (46,47).
 6. The device according to claim 1, wherein said selector slide(15) has at least one other switching position for forward drive (L) anda parking position (P).
 7. The device according to claim 1, wherein inneutral position (N) and parking position (P) of said selector slide(15), pressurized medium from said switching components (1, 2) can beremoved via said selector slide (15) and pressure lines (49, 50) to apressurized-medium tank (51, 52), there being located between saidselector slide (15) and said pressurized-medium tank (51, 52) a drainingnozzle (53, 54).
 8. The device according to claim 7, wherein saiddraining nozzle (53, 54) is adjustable according to the temperature ofthe transmission in a manner such that the discharge time of saidswitching components (1, 2) is constant over a definite range of thetemperature of the transmission.
 9. The device according to claim 3,wherein the pressure supplied via said selector slide (15) to theselected switching component (1 or 2) is fed by a clutch pressure valve(16) whereby operating with a closed one of said switching component (1,2) a pressure dependent on an engine torque is presettable.
 10. Thedevice according to claim 9, wherein the output pressure of said clutchpressure valve (16) and the output pressure of said load pressure valve(19) can be regulated by pressure regulators (17, 21) designed aselectromagnetically adjustable proportional valves.
 11. The deviceaccording to claim 1, wherein the shift from the neutral position (N) toone of the forward drive position (D, L), and the reverse drive position(R) can be electrically determined by an electronic control.